Isoflavone C-glycosides isolated from the root of kudzu (Pueraria lobata) and their estrogenic activities

The chemical structures of six isoflavones (1-6) isolated from the kudzu root (Pueraria lobata) were elucidated on the basis of the NMR and MS analyses to be four isoflavone C-glycosides as 6 ''-O-alpha-D-glucopyranosylpuerarin (1), puerarin (2), 3'-methoxypuerarin (3), 6 ''-O-alpha-D-apiofranosylpuerarin (4), and two aglycons as biochanin A (5) and formononetin (6), respectively. The estrogenic activities of isolated compounds and related isoflavones were evaluated using a yeast two-hybrid assay. Genistein exhibited the highest activity among the evaluated compounds at 10(-6) M followed by daidzein (10(-5) M), baiochanin A (5) (10(-5) M), daidzin (10(-5) M), 3',4',7-trihydroxyisoflavone (10(-3) M), and formononetin (6) (10(-2) M). The isoflavone C-glycosides (1-4) and 4',7-dimethoxyisoflavone showed no activities. In these results, it was found that the addition of 8-C-glucose or 3'-hydroxyl group to daidzein skeleton, or the substitution of hydroxyl functions to methoxyl groups, decreased the estrogenic activity of daidzein, on the other hand, the addition of 7-O-glucose moiety had no influence on the activity. (C) 2012 Elsevier Ltd. All rights reserved.